Shoe-drum brakes for vehicles

ABSTRACT

Adjacent ends of opposed shoes of a shoe-drum brake are actuated to apply the brake by two separate single-ended hydraulic cylinders which are located between the shoe ends with their axes substantially parallel and of which at least one is floatingly supported by the shoes, and the cylinders are connected to separate sources of hydraulic fluid under pressure.

United States Patent 1191 Newstead et al.

[111 3,807,536 1451 Apr. 30, 1974 SHOE-DRUM BRAKES FOR VEHICLESInventors: Charles Newstead, Walsall; Andrew Charles Walden Wright,Lapworth, both of England Girling Limited, Birmingham, England Filed;Feb, 144 1972 Appl. No; 225,863

Assignee:

Foreign Application Priority Data Feb. 15, l97l Great Britain 4678/71u.s. Cl. 188/345, 188/363 1m. 01 B60t 11/10 Field of Search 188/345, 106P, 363, 364,

188/106 A, 106 R; 192/83; 60/54.6 B; 92/61 References Cited UNITEDSTATES PATENTS 2/1966 Carruth 188/345 8/1971 Miyajima 188/345 8 1956Sinclair 188/363 x Primary Examiner-George E. A. Halvosa Attorney,Agent, or Firm-Scrivener, Parker, Scrivener & Clarke ABSTRACT Adjacentends of opposed shoes of a shoe-drum brake are actuated to apply thebrake by two separate single ended hydraulic cylinders which are locatedbetween the shoe ends with their axes substantially parallel and ofwhich at least one is floatingly supported by the shoes, and thecylinders are connected to separate sources of hydraulic fluid underpressure.

1 Claim, D taw n kiaqre PATENTEDAPR 30 191 3807'. 536

SHEET 1 [IF 2 FIG].

1 SHOE-DRUM BRAKES FOR VEHICLES This invention relates to improvementsin shoe-drum brakes and is concerned with hydraulic actuating means forthe shoes of such brakes.

The usual actuator is a double-ended hydraulic cylinder in which worktwo pistons each adapted to engage an end of a shoe, fluid underpressure being fed to the space between the pistons from apedal-operated master cylinder or other source of pressure fluid.

A serious disadvantage of that arrangement is that in the event offailure of a pipe line leading to the wheel cylinder, or even of a sealin the cylinder, the brake is put out of action.

According to our invention the shoes of a shoe-drum brake are actuatedby fluid under pressure supplied from two separate pressure sources totwo separate single-ended hydraulic wheel cylinders which are locatedbetween the shoes with their axes substantially parallel and of which atleast one is floatingly supported by the shoes.

Both cylinders may be floatingly supported by the shoes or one may befixed to the back-plate of the brake.

With either arrangement the cylinders are preferably displaced in anaxial direction relative to one another, the closed end of each cylinderengaging directly, or through a short axial spigot integral with thecylinder, with the web of one shoe, and the web of the other shoe beingengaged by a piston-rod of substantial length projecting from the otherend of the cylinder.

The two cylinders are preferably arranged reversely or back-to-back, thelong piston-rod of one cylinder lying alongside the other cylinder sothat the overall transverse dimension of the actuator formed by the twocylinders can be kept to a minimum. This dimension can be reduced bymaking the long piston-rods of small diameter relative to the diameterof the cylinders to allow a large amount of overlap of the cylinders.

The cylinders can be arranged with their axes in parallel horizontal,vertical or inclined planes as required by the design of the rest of thebrake.

The two-sources of pressure fluid may conveniently be the two pressurespaces of a tandem master cylinder so that normally fluid is fed to bothwheel cylinders at the same pressure. Alternatively the two pressuresources may be two separate master cylinders operated simultaneously orindependently.

If the pipe line to either wheel cylinder should fail or- As the wheelcylinders operate independently the volume of fluid required to applythe brake by either cylinder is not affected by failure of the other sothat there is no additional pedal travel, and no need for a mastercylinder of more than normal size.

Slots of substantial axial length are formed in the outer ends of thespigot and piston-rod of each cylinder to receive inwardly projectinglugs on the shoe webs, the lengths of the slots preferably being greaterthan the maximum permissible outward movement of the adjacent shoe end.This avoids any risk of a floating cylinder becoming disengaged from theshoes due to wear of the shoe linings.

One practical design of brake embodying hydraulic actuating mechanismwith two floating wheel cylinders 2 in accordance with our invention isilustrated by way of example in the accompanying drawings in which: I

FIG. 1 is an end elevation with one half in section;

FIG. 2 is a vertical section on the line 2-2 of FlG. l; and

F l0. 3 is a section of the actuator on the line 33 of .FIG. 1.

The brake illustrated is of the well-known duo-servo type. Arcuate shoes1, 2 provided with friction linings 3 are articulated together at oneend by a strut 4 of which the effective length is automatically adjustedas the shoe linings wear by known mechanism indicated generally at 5. 1

When the brake is applied the shoes tend to be carried round with thebrake drum and one or other of the shoes, according to the direction ofrotation of the drum, anchors on a torque-taking pin 6 fixed in the stationaryback-plate 7 of the brake. The shoes ean be applied mechanicallyfor parking by a hand brake actuating a cable 8 which is brought inthrough an opening in the back-plate and over a rocking quadrant 9 'to acam 10 located between the shoe ends.-

The shoes are applied hydraulically for normal service braking by fluidunder pressure supplied from separate sources to two single-endedwheelcylinders 11 and 12 floatingly supported between lugs 13, 14 pro jectinginwardly from the webs of the shoes adjacent to the ends co-operatingwith the pin 6. The axes of the two cylinders are parallel to theback-plate.

Working in each cylinder is a piston 15 sealed by a 'lip seal 16 and anO ring 17 housed in an annular grooye in the cylinder bore. The pistonmay have an extension 18 at the end nearest the closed end of thecylinder to prevent tilting of the piston.

An axial spigot 19 projecting from the closed end of the cylinder 1 1has in its free end a slot of substantial axial length which receives aportion of the mg 13 on the shoe 1 within a notch in the lug, Apiston-rod 20 extends from the other end of the cylinder and has a simi=lar Slotted engagement with the lug 14 on the shoe 26 The other cylinder12 is of identical construction but i is reversed, the spigot 21 on theclosed end of that c'ylinder engaging with the lug 14 on the shoe 2while the piston-rod 22 engages with the lug l3 on'the shoe 1 As will beappreciated from HO. 1 the piston-rod of each cylinder is in verticalalignment with the other cylinder.

A spring 23 may be located in each cylinder between the piston and theclosed end of the cylinder to urge the cylinder and piston-rod intoengagement with the lugs on the shoes.

Fluid under pressure is supplied from separate sources through flexiblepipes connected to union sockets 24 from which passages lead to thepressure spaces in the cylinders.

ln a modification of the actuating means described above only one of thecylinders is floatingly supported between the shoe ends and the other isfixed to the Stationary back-plate of the brake.

The parallel disposition of the cylinders and their axial displacementrelative to one another can remain the same.

An advantage of a floating single-ended cylinder is that it appliesequal forces to the two shoes between which it is supported. If onecylinder is fixed the force and piston assemblies of which at least oneis floatingly supported by the shoes, and one end of each cylinderengages the web of one shoe and the web of the other shoe is engaged bya piston-rod of substantial length projecting from the other end of thecylinder. theassemblies being reversely arranged with the piston-rod ofone assembly alongside the cylinder of the other assembly and with thecylinders being constructed and arranged to radially overlap so that theoverall radial dimension of the two actuators is kept to a minimum.

1. An internal shoe drum brake comprising a backplate, a rotatable drum,arcuate shoes each including a web mounted on said back-plate andcarrying friction linings for engagement with said drum, and twoseparate radially displaced hydraulic actuators both located betweenadjacent shoe ends and connected to separate sources of hydraulic fluidunder pressure, wherein said hydraulic actuators comprise single-endedcylinders and piston assemblies of which at least one is floatinglysupported by the shoes, aNd one end of each cylinder engages the web ofone shoe and the web of the other shoe is engaged by a piston-rod ofsubstantial length projecting from the other end of the cylinder, theassemblies being reversely arranged with the piston-rod of one assemblyalongside the cylinder of the other assembly and with the cylindersbeing constructed and arranged to radially overlap so that the overallradial dimension of the two actuators is kept to a minimum.